Where might the Finnish/Volga-Ural DNA portion come from?

Re: Where might the Finnish/Volga-Ural DNA portion come from?

I just received my results yesterday: 68% British Isles, 19% Central European (both of which reflect my Scottish-German father and my mother's heavily English colonial ancestry), and then two mystery percentages: 7% Eastern European and 6% Finnish-Volga/Ural. I have documented all my German ancestry back to the 17th century (all concentrated in one part of Hesse), and a few lines back into medieval times, in which heavy doses of Polish, Ukrainian, Serbian, Hungarian, and Russian blood came in via marriages of women from those nations with German nobles. My question is, could these pieces of Eastern European/Western Russian DNA (if that's what they are) be handed down from those influences? I do have one mystery ancestress in my German lineage, who died in the 1630s, about whom we know nothing except that she first shows up in northeast Germany. If she was Polish or a Balt, would that necessarily show up as 6% almost 400 years later?

I forgot to add: there is a tradition in my mother's family of a great-great-grandmother having Cherokee blood. I've never been able to find it, though.